Isolated Supramolecular [Ru(bpy)3]-Viologen-[Ru(bpy)3] Complexes with Trapped CB[7,8] and Photoinduced Electron-Transfer Study in Nonaqueous Solution

The synthesis of two supramolecular diruthenium complexes, 1⊂CB[7] and 1⊂CB[8] (CB[n]=cucurbit[n]uril), which contain the respective host CB[7] and CB[8], were synthesized and isolated. In the case of host CB[8], the desired supramolecular complex was obtained by utilizing dihydroxynapthalene as a template during the synthesis. The 1H NMR spectra, electrochemistry, and photochemistry of these supramolecular complexes were performed in nonaqueous solution. The results show that both CB[7,8] hosts mainly bind to the linker part in solution in acetonitrile. This binding also lowers the oxidation potential of the ruthenium metal center and hinders the quenching effect by the viologen moiety. It has also been shown that external methylviologen can be included into 1⊂CB[8]. Analysis with NMR spectroscopy, electrochemistry, and photochemistry clearly shows a viologen radical dimer formation between the bound viologen and free methylviologen, thereby showing that the unique abilities of the CB[8] host can be utilized even in nonaqueous solution. Supramolecular sandwich: Supramolecular systems of CB[7] and CB[8] (CB[n]=cucurbit[n]uril) locked between two redox‐active [Ru(bpy)3] (bpy=2,2′‐bipyridine) complexes have been isolated from aqueous solutions and their electrochemical and photochemical properties have been studied in organic solvent (see scheme).